1. Field of the Invention
The present invention relates to a target supply apparatus using for an extreme ultraviolet light source apparatus which generates an extreme ultraviolet (EUV) light from a plasma generated by irradiating a target with a laser light.
2. Description of the Related Art
In recent years, along with a progress in miniaturization of semiconductor device, miniaturization of transcription pattern used in photolithography in a semiconductor process has developed rapidly. In the next generation, microfabrication to the extent of 65 nm to 32 nm, or even to the extent of 30 nm and beyond will be required. Therefore, in order to comply with the demand of microfabrication to the extent of 30 nm and beyond, development of such exposure apparatus combining an extreme ultraviolet (EUV) light source for a wavelength of about 13 nm and a reduced reflective optics is expected.
As the EUV light source, there are three possible types, which are a laser produced plasma (LPP) light source using plasma generated by irradiating a target with a laser beam, a discharge produced plasma (DPP) light source using plasma generated by electrical discharge, and a synchrotron radiation (SR) light source using orbital radiant light. Among these light sources, the LPP light source has such advantages that luminance can be made extremely high as close to the black-body radiation because plasma density can be made higher compared with the DPP light source and the SR light source. Moreover, the LPP light source also has an advantage that strong luminescence only with a desired wavelength band is possible by selecting a target material. Furthermore, the LPP light source has such advantages that there is no construction such as electrode around a light source because the light source is a point light source with nearly isotropic angular distributions, extremely wide collecting solid angle can be acquired, and so on. Accordingly, the LPP light source having such advantages is expected as a light source for EUV lithography which requires more than several dozen to several hundred watt power.
In the EUV light source apparatus with the LPP system, firstly, a target material supplied inside a vacuum chamber is excited by being irradiated with a laser light and thus be ionized to become plasma (cf. Japanese patent application Laid-Open No. 2007-266234). Then, a cocktail light with various wavelength components including an EUV light is emitted from the generated plasma. Then, the EUV light source apparatus focuses the EUV light by reflecting the EUV light using an EUV collector mirror which selectively reflects an EUV light with a desired wavelength, e.g. a 13.5 nm wavelength component. The reflected EUV light is inputted to an exposure apparatus. On a reflective surface of the EUV collector mirror, a multilayer coating with a structure in that thin coating of molybdenum (Mo) and thin coating of silicon (Si) are alternately stacked, for instance, is formed. The multilayer coating has performance of a high reflectance ratio (of about 60% to 70%) with respect to the EUV light with a 13.5 nm wavelength.
In the conventional target supply apparatus, a target is supplied by pressurizing the inside of the tank in the target supply apparatus with gas from a gas cylinder. However, when there is no need to output the EUV light such as during wafer replacement and adjustment of the exposure apparatus or of the EUV light source apparatus, then the supply of the target is not needed. Therefore, the supply of the target when there is no need to output the EUV light becomes waste of the target.